OPN4 and depressive symptom measurement: This study therefore objectively determined the mean daylight and daily hourly light exposure and duration of exposure to illumination levels recommended for light therapy in depression (15) in a group of patients with non-seasonal depression and healthy participants, and quantified melanopsin function with an optimized pupillometric paradigm that is robust to the presence of subtle melanopsin defects at early stages of retinal disease (16, 17).